Question

Explain giving one example for each of the following chemical changes :

(a) Double decomposition

(b) Thermal dissociation

(c) Reversible reaction

(d) Displacement reaction

Answer 1

a) Double decomposition Reaction: Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

$AgN{O}_3$ + $NaCl$ $\to$ $AgCl$ + $NaN{O}_3$

Silver nitrate sodium chloride white precipitate sodium nitrate

(silver chloride)

(b) Thermal dissociation is the breaking apart of a molecule's bonds due to the introduction of heat. Or Thermal dissociation is a simple, single-step reaction where a molecule splits into two products. Usually, only one bond breaks and the reaction is reversible.

$H_{2}O$ $\to$ $H_2$ + $O_2$

c) Reversible reaction - A reversible reaction is a chemical reaction where the reactants form products that, in turn, react together to give the reactants back. Reversible reactions will reach an equilibrium point where the concentrations of the reactants and products will no longer change.

$N{H}_{4}C{l}_{\left(s\right)}$ $N{H}_3\left(g\right)$ + $HC{l}_{\left(g\right)}$

d) Displacement reactions - The chemical reactions in which a more reactive element displaces a less reactive element from a compound are known as displacement reactions. For example,

i) $Z{n}_{\left(s\right)}$ + $CuS{O}_{4\left(aq\right)}$ $\to$ $ZnS{O}_{4\left(aq\right)}$ + $C{u}_{\left(s\right)}$ .

ii) $C{u}_{\left(s\right)}$ + $2AgN{O}_{3\left(aq\right)}$ $\to$ $Cu(N{O}_3{)}_{2\left(aq\right)}$ + $2A{g}_{\left(s\right)}$.